Conventionally, driving sources such as an internal combustion engine and an electric motor, and wheels and the like are coupled via a drive transmission system having a reduction gear and the like, so that motive power is transmitted from the driving source through the drive transmission system to the wheels. However, in the drive transmission system coupled to the driving source, for example, “jara” sounds and muffled sounds are produced by torsional vibration resulting from rotation fluctuations caused by torque fluctuations in the internal combustion engine.
“Jara” sounds are abnormal sounds called “jarajara” caused by collision of an idling gear pair of a transmission gear set by the torsional vibration resulting from rotation fluctuations caused by torque fluctuations in the internal combustion engine. Furthermore, muffled sounds are abnormal sounds generated within a vehicle cabin by vibration caused by torsional resonance of the drive transmission system that results from torque fluctuations in the internal combustion engine. Torsional resonance of the drive transmission system exists in a normal region, for example.
A torsional vibration damper is conventionally known, by which a driving source such as an internal combustion engine and an electric motor, and wheels and the like are coupled to transmit rotation torque from the driving source while absorbing torsional vibration between the driving source and a drive transmission system having a transmission gear set (for example, see WO 2011/067815 (PTD 1)).
This torsional vibration damper includes a cam portion having a cam surface at its outer periphery and configured such that the curvature of the cam surface changes in the circumferential direction; a disk plate provided coaxially with the cam portion and rotatable relatively to the cam portion; and an elastic member provided between the cam portion and the disk plate and elastically deformed during relative rotation of the cam portion and the disk plate.
Furthermore, this torsional vibration damper includes an arm member having one end coming in contact with the cam surface of the cam portion and the other end biased by the elastic member. When the cam portion and the disc plate relatively rotate, this arm member rotates about the rotation shaft provided on the disk plate to elastically deform the elastic member, thereby transmitting rotation torque between the cam portion and the disk plate.
According to this torsional vibration damper, the arm member is swung in accordance with rotation of the cam portion to elastically deform the elastic member, so that the range of the torsion angle of the cam portion and the disk plate can be widened. Accordingly, the torsional rigidity of the cam portion and the disk plate can be entirely decreased, thereby sufficiently attenuating “jara” sounds and muffled sounds to allow improvement in vibration damping performance.